Carbonatation is used in a variety of different processes to remove impurities such as, but not limited to, unwanted ions or high molecular weight compounds from liquids. The processes generally involve the addition of a metal or ammonium hydroxide whose carbonate is as least partially insoluble under the conditions employed. Carbon dioxide (CO2) is also added, resulting in the formation of an insoluble carbonate as a precipitate which may be separated from the liquid, for example by filtration.